[alsa-devel] Issue in alsa when dma complete race with pcm release

[Lars-Peter Clausen]

On 07/03/2015 10:25 AM, Shengjiu Wang wrote:
> Hi alsa-devel
>
>     There maybe a issue in ALSA when dma complete race with snd_pcm_release.
> The pcm release and dma complete are in different thread. There is occasion
> that dmaengine_pcm_dma_complete() is called too late, some memory has been
> freed, the prtd is null. Then there is kernel dump.
>
>     Is there any solution for this issue? Thanks.

We need to introduce a synchronization primitive that allows a dmaengine 
client to synchronize to the execution of the complete callbacks.

terminate_all() unfortunately can't do this since terminate_all() might be 
called from within one of the complete callbacks and so would cause a 
deadlock if we'd wait for all complete callbacks to finish before 
terminate_all() returns.

So what is needed is a new function called dmaengine_sync() that will wait 
until all scheduled complete callbacks have finished. A call to this 
function needs to be put in snd_dmaengine_pcm_close() before the prtd is closed.

- Lars